1. Field of the Invention
The present invention relates to a capacitive current-sharing control circuit, and more particularly to a capacitive current-sharing control circuit which is used to provide a stable current source to LED lamp strings.
2. Description of Prior Art
A LED (light emitting diode) is a current-driving element and which has a characteristic of low-voltage unidirectional conduction. In addition, luminous flux variation of the LEDs varies with the current flow through the LEDs. Hence, it is essential to provide a stable current source to the LEDs, thus maintaining illuminating brightness of the LEDs.
At present, the current mirror is the most commonly used and simple current-sharing control circuit for the LEDs. As shown in FIG. 1 which is a circuit diagram of a prior art LED array circuit. The LED array includes a plurality of LED lamp strings 40 and a plurality of current mirrors 50, which are composed of a plurality of BJTs. In order to ensure that the current mirrors 50 are in proper operation, it is important to ensure that the characteristics of the BJTs are identical and each of the BJTs is operated in the active region.
However, due to different forward turn-on voltages of the light emitting diodes and different driving voltages of the BJTs, it is probably that the driving voltage of the current mirrors is less than the operating voltage in the active region. Hence, the currents flow through the LED lamp strings 40 are not the same, and this will result in different illuminating brightness of the LED lamp strings 40.